Dibenzylamine does not form any carcinogenic nitrosamines and can be used as a starting compound for manufacturing the vulcanization accelerator tetrabenzylthiuram disulfide, which also forms only nitrosamines of low volatility that remain in the rubber. The manufacture and use of this vulcanization accelerator is therefore largely harmless to health.
Dibenzylamine is specifically manufactured by hydrogenation of benzonitrile with Pt catalysts (U.S. Pat. No. 3,923,891). Other suggested syntheses for dibenzylamine start with benzylamine (Synthesis (1), 70 (1979); J. Organomet. Chem. 208 (2), 249 (1981); Chem. Lett. (6), 889 (1984); Ind. J. Technol. 23 (7), 266 (1985)). In addition, dibenzylamine occurs as a byproduct in the industrial synthesis of benzylamine from benzaldehyde by reaction with ammonia and catalytic hydrogenation with Raney nickel (Ullmanns Encyclopadie der technischen Chemie, 4th edition, Volume 8, 440): EQU C.sub.6 H.sub.5 --CHO+NH.sub.3 +H.sub.2 .fwdarw.C.sub.6 H.sub.5 --CH.sub.2 NH.sub.2 +H.sub.2 O EQU C.sub.6 H.sub.5 --CH.sub.2 NH.sub.2 +C.sub.6 H.sub.5 --CHO.fwdarw.C.sub.6 H.sub.5 --CH.sub.2 N.dbd.CH--C.sub.6 H.sub.5 +H.sub.2 O EQU C.sub.6 H.sub.5 --CH.sub.2 N.dbd.CH--C.sub.6 H.sub.5 +H.sub.2 .revreaction.C.sub.6 H.sub.5 --CH.sub.2 NHCH.sub.2 --C.sub.6 H.sub.5
Dibenzylamine is therefore formed via the stages of monobenzylamine and N-benzylbenzylidenimine and can be separated from the intermediate reaction mixture by fractionation. The reaction mixture can also contain tribenzylamine as a secondary product, and benzyl alcohol and toluene as reduction products of benzaldehyde. According to Ullmanns Encyclopadie, Volume 8, Page 440, in the reaction a mixture of 470 kg monobenzylamine, 2 kg benzylbenzylidenimine, 1 kg dibenzylamine, and 1 kg benzyl alcohol is obtained, for example, from 500 kg of benzaldehyde (4.72 mol) and 110 kg ammonia (6.47 mol)--in other words, with a stoichiometric excess of ammonia at 100.degree. C.
In addition, J. Amer. Chem. Soc. 61 (1939), Page 3566 describes the manufacture of monobenzylamine with dibenzylamine as a byproduct, by reacting benzaldehyde with a mere stoichiometric excess of ammonia under conditions of catalytic hydrogenation with Raney nickel as the catalysts. According to the example cited therein, a mixture of 287 g monobenzylamine and 21.7 g dibenzylamine is obtained from 3 mol benzaldehyde and 3 mol ammonia--in other words, using stoichiometric amounts relative to monobenzylamine formation, but using a stoichiometric excess of ammonia relative to dibenzylamine formation, at 70.degree. C. On the other hand, according to Table 1 of this citation, the amount of dibenzylamine can predominate (80.8% versus 11.8% monobenzylamine) when using stoichiometric amounts of benzaldehyde and ammonia (1/2 equivalent) relative to dibenzylamine formation.